The present invention relates to illuminating devices which can be suitably employed as vehicular lamps. Particularly, the invention concerns a vehicular lamp of a type which employs light-emitting diodes as its light source and which has an improved illumination effect.
Furthermore, the invention relates to such a vehicular lamps which can be suitably employed as a high-mount stop lamp and in which a lamp body thereof can be installed on different vehicle bodies merely by changing a mounting member of the lamp.
Recently, light-emitting diodes having a high luminance output have become available at a relatively low cost. Such light-emitting diodes have been considered as light sources for vehicular lamps such as brake lamps, tail lamps, and so-called "high-mount" stop lamp installed on the outside (or inside) of the rear part of a vehicle.
Light-emitting diodes are advantageous in such applications in a number of respects. First, since light-emitting diodes, unlike ordinary electric light bulbs, have no filament, their service life is semipermanent. Also, since the light-emitting diodes are free from filament burn out, it is seldom necessary to replace a diode. Still further, the mounting arrangement of light-emitting diodes can be relatively freely chosen in a vehicular lamp. That is, because of their small size, the thickness of the lamp can be reduced, and therefore the lamp can be easily mounted on the body of the vehicle. Further the lamp can be miniaturized due to the use of light-emitting diodes. Moreover, the amount of heat generated by a light-emitting diode is much smaller than for an ordinary light bulb of similar light output.
FIG. 1 shows a conventional vehicular lamp using light-emitting diodes. In FIG. 1, reference numeral 1 designates a front lens member on the inside of which a number of closely spaced diffusion lenses 2 (small convex lenses) are formed; 3, a printed circuit board disposed inside the front lens member 1; 4, a plural number of light-emitting diodes arranged at predetermined intervals on the printed circuit board 3; 5a and 5b, conductive metal foils; 6, lead wires; and 7, a diode segregating member arranged on the printed circuit board 3. The diode segregating member 7 is used to separate the light-emitting diodes 4 from one another. The diode segregating member 7 has a number of diode accommodating chambers 8 into which the light-emitting diodes 4 are received. The diode accommodating chamber 8 are each, for instance, in the form of a tapered hole, and the walls thereof serve as reflecting surfaces 9 so as to effectively utilize the light outputs from the diodes and to improve the illuminating efficiency.
In the conventional vehicle lamp thus constructed, the light output from each light-emitting diode 4 is reflected by the reflecting surface 9 to convert the point-light-source light to planar light. The planar light is then diffused by the diffusion lenses 2. However, when looking straight at the front lens member 1, it is possible to see the front surface 7a of the diode segregating member 7 through the front lens member 1 because of light refraction. Therefore, when the lamp is turned on, the surface of the front lens member 1 is not uniform in brightness; that is, the lamp does not provide uniform illumination.
This difficulty may be overcome by arranging adjacent ones the light-emitting diodes close to one another, but at the expense of increasing the number of light-emitting diodes. Furthermore, if the diodes are arranged excessively close to one another, the quantity of light emitting is actually decreased due to the accompanying increase in temperature (the output of a light-emitting diode decreases with increasing temperature).
In general, different vehicular lamps must be manufactured for different models or types of vehicles, and different types of lamps are installed at different positions on a vehicle. Therefore, lamps for one model of a vehicle or one location on a vehicle cannot be used for another model or location; that is, in general, vehicular lamps are not interchangeable. Further, in a vehicular lamp such as a high-mount stop lamp which is ordinarily installed by the user rather than the manufacturer of the vehicle, it is particularly uneconomical to manufacture and store different types of lamps for different models of vehicles. If such a lamp is manufactured for only one vehicle type, in the case where the user trades in his old automobile for a new automobile of a different model, he cannot use the lamps from the old automobile on the new automobile. Accordingly, there has been a strong demand for the provision of a vehicular lamp which can be installed on any model of vehicle merely by changing a few components thereof, and in which the lamp body is common for all models of vehicles.